What happens when it’s 15 degrees outside, and your furnace is on the fritz?

Whose fault is it? The furnace manufacturer, or the contractor you hired to install it?

Many contractors are quick to blame problems on defective equipment. But a surprising number of the contractors we interviewed admitted that manufacturer defects aren’t the biggest culprit when a heating system dies before its time. Preventable installation errors and even simple lack of maintenance are just as likely to cause problems.

An analysis of more than 1,500 negative furnace reviews showed that homeowners consistently complain about 5 problematic furnace parts:

Why do those parts break so frequently? And, perhaps more importantly, how can homeowners spot potential defects or installation problems?

Blower motors

“I haven’t seen too many manufacturer errors with blower motors,” said Joel Biagi, a service department manager with a local heating company in Meridian, Idaho.

Inadequate ductwork is the most common installation error Biagi sees, and it’s a problem because it restricts airflow to the system. This means the blower motor works too hard, shortening its lifespan.

Sometimes your contractor may install the ductwork badly, and sometimes they may simply fail to correct existing problems. Ductwork should be thoroughly examined when a new furnace is installed. Perhaps it was installed badly to begin with, or perhaps the heating needs of the house have changed in the years since the first system was installed.

But homeowners themselves can also be their blower motor’s worst enemy. Failure to regularly change the filters restricts airflow even if the ductwork is adequate, and the result is an air-starved system and a burned-out blower motor.

Control boards

“If I put 1,000 heaters in, usually we don’t have a problem with the control board unless it gets wet,” said Steve Nevrotski, owner of SGN Mechanical in Philadelphia.

Like blower motor failure, water damage can also be caused by lack of airflow. Sometimes air conditioning units are installed on top of furnaces. If the cooling system’s coils don’t get enough air, they can freeze up. Once they start to thaw, the resulting water can overflow the drain pan under the coils and spill over into the electrical systems, causing the control board to short circuit.

Factory defects are unlikely. Nevrotski said the control boards are all tested before they leave the factory, and the only thing that could cause failure aside from water damage is incorrect wiring. But how likely is that?

“You only have two wires—red and white,” said Nevrotski. It’s theoretically possible to wire the system incorrectly, but it would be pretty hard to get confused with only two wires. Even then, Biagi said newer furnaces have safety measures installed, so a shorted wire only blows a fuse, instead of blowing out the whole control board.

Heat exchanger

What usually causes a heat exchanger to break? It turns out heat exchanger problems can be caused by the installer, the manufacturer, or even the homeowner.

“I’m going to lean toward lack of maintenance,” said Justin Zocchi, owner of Race City Heating and Air in Moorseville, North Carolina. A good technician will monitor the system’s temperature rise to make sure the furnace isn’t running too hot, which can damage the heat exchanger. With a condensing furnace, clogged drains will also cause premature failure of the heat exchanger, Zocchi said.

Once again, Nevrotski cited homeowner neglect as a threat. “If you don’t change the filter, you’re not letting enough air go across it. It will overheat, and the heat exchanger will crack,” he said.

But there can be problems at installation time too. Biagi said elevation effects gas pressure, so technicians should check the gas pressure to see if an adjustment should be made to the factory default setting. With some newer furnaces, you can check the gas pressure but you can’t adjust it. In those cases, Biagi said it’s necessary to replace the gas valve to get the right amount of pressure.

Factory defects are not out of the question. Some manufacturers do have problems with heat exchangers, acknowledged Nevrotski, but usually a well-maintained furnace will not have heat exchanger problems for at least 20 years.


Ignitors are hard to break, said Biagi. “If it was to go out it would be wear and tear or manufacturer defect,” he said. Wear and tear can be accelerated by environmental conditions such as moisture in the basement, and Nevrotski said sometimes household chemicals stored near the furnace can evaporate, creating gasses that burn the ignitor out.

Dust can also be an issue, but Zocchi said sometimes you can install the ignitor vertically instead of horizontally so it collects less dust.

Pressure Switch

Pressure switches are a little different from the parts listed above because they function as a safety measure, meaning their purpose is to shut the system down if there’s a problem.

There is a long list of things that can trip the pressure switch on a furnace. Biagi said the PVC pipe used in some flues will produce plastic particles similar to sawdust if cut with a sawzall, and the particles can plug up the pressure switch. This is an installation error caused by carelessness. A blocked chimney will also trip the pressure switch, and Nevrotski said even a flue pipe that is too long or is not pitched back toward the furnace will cause pressure switch issues because the flue won’t draw correctly.

Lack of regular maintenance can also be a factor. Zocchi said the ports on a furnace have to be cleaned regularly. Some furnace brands, like Lennox and Goodman, have smaller ports and need more frequent cleaning.

A Reply from a Distributor

“I probably get a little defensive when you mention factory defects,” said John Zdon, a field service representative for Lyon, Conklin & Co. in King of Prussia, Pennsylvania. His company is the sole distributor of Trane and American Standard furnaces in the Mid-Atlantic region.

Zdon said that when multiple problems with the same piece of equipment come to light, Trane and other manufacturers investigate the problem. If a part is determined to have a problem, a recall is issued, just like when car manufacturers discover a problem with a certain model. So an isolated manufacturer defect is very unlikely.

Instead, installer errors are the more likely scenario, from Zdon’s perspective. “There’s more than one way to do a job, but there’s certain things you can’t violate,” he said.

Zdon said improper ductwork is the culprit most of the time. “Very rarely does an installer go out and really look at ductwork,” he said. Ductwork issues cause a slew of problems, including several on our list—blower motor failure and cracks in the heat exchanger. Electrical problems are also a common problem, causing ignitor failure and other issues. Zdon agreed that water can cause problems with control boards, and said water can have another effect–when heavy pipes aren’t property supported, their weight can cause cracks in the system.

How do you Avoid Installation Errors?

We’ve seen that installation errors aren’t the only culprit when a heating system fails prematurely. Environmental factors, maintenance and even factory defects can play a role. But preventing installation errors is more than half the battle.

So how can the average homeowner, without training in heating replacements, prevent these common problems?

The most important thing to choose your contractor wisely. We recommend that you check your contractor’s references. It may be tempting to hire someone who can do your job inexpensively, but beware of contractors who moonlight as HVAC system installers on the side.

“Somebody’s brother or somebody’s cousin knows this guy and he can do it a thousand dollars cheaper than anyone else,” said Dave Keiser, president of Keiser Mechanical Services in Northern New Jersey. “They stick it in and get it going and get paid and that’s it.” These jobs are easily recognizable to Keiser because there’s no sticker on the furnace, whereas most professionals label each unit they install with their company name and the date of installation. “Someone who’s not proud of their work never puts a sticker on it,” he said.

Asking the right questions is also helpful. For example, homeowners should make sure their contractors are performing a load calculation to determine exactly what size furnace is necessary. Sean Kazmi, president of AAA HVAC Services in Herndon, Virginia, said many companies automatically replace older furnaces with a unit that’s exactly the same size. They assume the old unit was the right size, but upgrades to the house like new windows or a new roof may have made it more heat-efficient in the years since the furnace was installed. You might not need as large a unit any more.

“If you have too big a furnace, your gas and electric bills will be higher,” Kazmi said. A homeowner with an unnecessarily large furnace might pay higher bills for years, never knowing they could have gotten by with a smaller furnace.

What if your furnace is too small? Well, then you’ll be cold, Kazmi said.

Another red flag is a contractor who doesn’t plan to get a permit for working on your HVAC system. In most cases, a permit requires the state or city to send out an inspector to look at the completed job. When you get an inspection, you are guaranteed that the system is installed properly and up to local and national code standards.

Get your contractor to explain your ductwork

Over and over again, we heard that poor ductwork is the heart of many furnace problems. Our ductwork specialists say that too many bends in the ductwork will cause problems, as will an exhaust pipe installed too close to an intake pipe. Sometimes this causes the furnace to act finicky, working well some of the time but misfiring or refusing to start on days when the wind is blowing in a certain direction.

We have seen a lot of bad installations where the return vent is in the basement next to the gas appliances, which can draw carbon monoxide fumes into the house. Carbon gases can be pulled back down through the return because it’s stronger than the natural draft of the chimney.

Homeowners can prevent this problem making sure the return vent is in not in the basement near the appliances, but on the first floor. The ideal is to have the return installed in the conditioned space.

Chimney liners are another big source of problems. High-efficiency heaters must be vented out through the wall, bypassing the chimney entirely. But lower efficiency heaters that vent through an older chimney often don’t create enough heat to keep condensation from forming in the chimney. Over time, the condensation can eat away at brick and mortar, causing your chimney to deteriorate. In addition, Jackson said condensation in the chimney can cause premature failure of your furnace’s heat exchanger. In such situations, a liner might be a good idea.

But we have seen many cases where the chimney liner is too small. It’s a common scenario—a square chimney measuring 8 or 12 inches is suddenly much smaller once it’s lined. Now you have fewer square inches in the chimney, and it’s not allowing the exhaust flue gasses to escape. Newer furnaces have sensors on them that detect excess flue gasses and automatically turn the furnace off as a safety precaution.

A too-small chimney cap can also cause problems, trapping exhaust fumes in the chimney. In extreme cases, carbon monoxide gas can even be pushed back into the home, although Keiser said that would be unusual. The chimney would have to get almost pressurized to push the CO gas into the home.

There are standard calculations that will determine what size chimney liner is needed… We figure you need a chimney liner that’s equal in diameter to the sum of all the pipes that are feeding into it. For example, if you have a six-inch flue pipe for the furnace and a 3-inch pipe for the hot water heater, you need a chimney liner that’s at least 9 inches in diameter. Otherwise, “It’s like three lanes of traffic merging into one.

In many cases, you need a separate contractor to install the chimney liner. That means getting multiple quotes and vetting another round of contractors, but it’s worth it. It’s too big an investment to take lightly.

Make An Informed Choice

When you spend a fortune on a new heating system, you want to feel confident that it will be there when you need it. It’s daunting to think of all that can go wrong–everything from installation errors to factory defects to maintenance issues. Some of those problems can’t be prevented, but most of them can be avoided as long as you’re attentive.

Vetting your contractor carefully and asking the right questions can prevent many installation errors. Factory defects will most likely trigger a recall, and the defective part will be replaced by the manufacturer.

That leaves regular maintenance, and that’s your responsibility as the homeowner. Bringing your technician in for an annual tune-up is essential, but you should also find out how often the filter needs to be changed. The best ductwork in the world won’t draw enough air if the filters are allowed to get dirty, and we’ve seen how lack of airflow can choke a system. Figure out a routine for remembering to change the filter, like changing it every time you make a monthly mortgage payment, or setting up an alert in an online calendar that will send you an email when it’s time.

Your careful research will pay off. When it comes to furnaces, an informed homeowner is a warm homeowner.

Learn more about our Furnace installation and repair services.

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Original article on www.furnacecompare.com


  1. I think it has something to do with the heat exchangers. We’ve already encountered that in the cooling towers..

    Cooling Tower Australia

  2. I think it has something to do with the heat exchangers. We’ve already encountered that in the cooling towers..

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